Flow-Through Fluid Purification Device

ABSTRACT

A flow through fluid purification device ( 1 ) comprising a container ( 5 ) arranged such that fluid can flow through a volume ( 8 ) of the container ( 5 ) from an inlet ( 3 ) to an outlet ( 7 ), and an inner cylinder ( 10   a ) inserted or insertable into the volume ( 8 ) of the container ( 5 ) and defining an interface wall ( 11 ) permeable for radiation with a wavelength in the UV-range, preferably between 150 nm and 200 nm, wherein the container ( 5 ) includes plurality of axially arranged cylinder parts ( 5   b,   5   c,   5   d,   5   e ) connected to each other by welding to form an outer cylinder assembly ( 5   a ).

The invention relates to a flow-through fluid purification device forpurifying a fluid, preferably by oxidizing organics contained in pure orultra-pure water. The invention also preferably relates to suchflow-through fluid purification devices that are designed for laboratoryscale water purification applications with a maximum throughput volumeof 2 l/min.

BACKGROUND

Devices are known which provide the possibility to purify a fluid,preferably to produce pure or ultra-pure water, by oxidizing organicscontained in the fluid in that the fluid is exposed to UV-C radiationwhile it flows through a container of the device.

Ultrapure water can be defined as the highest quality reagent gradewater that exceeds ASTM D5127 standards and that has a total organiccarbon (TOC) of less than 5 parts per billion (ppb).

UV radiation according to DIN 5031 part 7 is defined as radiation havinga wavelength in a range between 100 nm and 380 nm. A sub range of thisrange including wavelengths shorter than 280 nm is the UV-C range and afurther sub range including wavelengths shorter than 200 nm is thevacuum UV-C range (VUV).

The purification, to which the present invention pertains, aims atreducing the TOO content in the fluid flowing through the device throughorganic oxidizing reactions induced by the UV-C radiation.

Common flow-through purification devices which are based on oxidation byUV radiation are using, as a radiation source, a mercury gas lamp. Thelamp is arranged such that it irradiates the fluid flowing through acontainer. In the oxidation reaction induced by the UV-irradiation theorganics contained in the fluid are degraded into carbonates andbyproducts comprising intermediate ions other than carbonates and whichcan be filtered out of the fluid after purification. The oxidizingreaction includes an intermediate step of decomposing water moleculesinto different reactive intermediates including radical, neutral andionic intermediates. The radical intermediates subsequently oxidizeorganics contained in the fluid into carbon dioxide and water. UV-lightwith a wavelength of 185 nm is known to effectively generate suchradical intermediates.

It is also known to use excimer lamps for germicidal water purification.Such lamps are based on the excitation of, for example, a xenon gas toan excimer state. The wavelength of the radiation emitted duringexcitation and de-excitation is 172 nm or below (depending on the gasused in the lamp). This wavelength is too low to be directly used forwater purification applications and it has a very low watertransparency.

WO 2014/148325A1 discloses to use such excimer lamp in combination witha translucent coating on the lamp to shift the emitted wavelength tohigher wavelengths. The additional coating adds, however, to the cost,has a reduced lifetime due to a degradation of the coating with time dueto UV-exposure, and has a reduced performance because the coatingabsorbs around 50% of the radiation and restitutes only 50% of theabsorbed energy.

WO 95/15294A1 discloses a sterilizer for water and other fluids thatutilize ionizing UV-radiation as a sterilizing means. A cylindrical UVlamp as a radiation source is centrally housed in a tubular air chamberwhich in return is positioned coaxially within the interior of a housingforming an elongate exposure chamber through which the fluid flows froman inlet at one axial end portion to an outlet at an opposite axial endportion. An array of baffles in the form of coaxially disposed toroidaldisks spans the interior of the exposure chamber with each baffle partlyblocking the passage of fluid as it flows through the chamber along theaxial extension. Each baffle is provided with a channel between the edgeof the baffle and the inner peripheral wall of the chamber to permitfluid to flow past the baffle at a portion adjacent to the chamber walland the channels of neighboring baffles are offset from each other togenerate a sinuous and turbulent flow of the fluid as it traverses thelength of the chamber. Thus, the fluid stream is sequentially divertedtowards and away from the radiation source. An air channel may bechanneled through the air chamber for the co-production of ozone and theozone may in turn be reacted with the water either prior or subsequentto the treatment of the water with the UV radiation. In thisflow-through device significant portions of the fluid to be purified canpass through the device with relative large distances from the radiationsource, thereby potentially suffering from incomplete purification.

The document US 2007/0003430A1 discloses a method of inactivatingmicroorganisms such as viruses within a fluid. The inactivating processis based on the use of an elongated UV lamp emitting radiation between180 and 320 nm, preferably between 225 and 290 nm, surrounded by anelongated reaction chamber through which a primary flow directed alongthe length of the UV lamp is generated from an inlet to an outlet. Acirculating secondary flow is superimposed on the primary flow and both,the primary and secondary flow, are generated by a rotating agitatordisposed within the reaction chamber or by a spiral wound tubesurrounding the UV lamp and defining a helical channel that spiralsaround the UV lamp and approaches but does not engage the UV lamp andhas a D-shaped cross section. This flow-through purification isrelatively complex and has high manufacturing costs.

The prior art purification devices using UV radiation frequently employmercury based UV lamps to produce the desired wavelength radiation.Mercury based UV lamps, are, however, generally problematic as theyrequire extreme care in handling and special treatment or disposalprocedures due to the hazardous nature of the mercury.

Existing flow-through fluid purification devices commonly have thecontainer formed from a unitary cylindrical body. Since different puritylevels require different effective radiation exposure levels and/oroxidation duration which—in view of the flow-through concept of suchdevices—requires different reactor lengths, the cost of creatingdifferent devices for different purity levels is high.

Further, the existing devices frequently require complicated structuresin order to mount the radiation source into the device and maintenancecan be problematic.

Object of the Invention

An object of the invention is to provide a flow-through fluidpurification device for purifying a fluid, preferably to produce pure orultra-pure water, which can be simplified and produced at low costand/or facilitates maintenance, can be adapted to different purificationlevels and can provide a high purification efficiency.

Solution of the Problem

According to the present invention this object is solved by providing aflow-through fluid purification device with the features of claim 1.Preferred embodiments are defined in the dependent claims.

The flow through fluid purification device of the present inventioncomprises a container arranged such that fluid can flow through a volumeof the container from an inlet to an outlet, and an inner cylinderinserted or insertable into the volume of the container and defining aninterface wall permeable for radiation with a wavelength in theUV-range, preferably between 150 nm and 200 nm, wherein the containerincludes a plurality of axially arranged cylinder parts connected toeach other by welding to form an outer cylinder assembly.

In that the outer cylinder assembly is formed by welding the axiallyarranged cylinder parts together cost advantages with respect tomanufacturing and maintenance can be realized. Further, a range ofscaled purification devices with different size, capacity and throughputcan be created and produced with a small number of different componentsin a modular construction. Devices which have a larger axial length ofthe oxidation zone to achieve a higher purification level of thepurified water at the outlet can be produced by simply adding/stackingfurther cylinder parts to the cylinder assembly.

The device can be pre-fabricated without the inner cylinder as aself-supporting unit and the radiation source for purifying the fluid,for example an excimer lamp, can be subsequently inserted into the innercylinder and also removed for maintenance.

In a preferred embodiment the device has one end cap engaged with anopen axial end of the outer cylinder assembly to fluid tightly close thevolume of the container at the end where the end cap is arranged and tohold the inner cylinder in position in the outer cylinder assembly. Inanother embodiment the device has two end caps, each one engaged withone of the two open axial ends of the outer cylinder assembly to fluidtightly close the volume of the container at the ends, wherein at leastone of the two end caps is arranged to hold the inner cylinder inposition in the outer cylinder assembly.

In that the axial ends of the outer cylinder assembly are closed by endcaps (one could be sufficient if the other end is permanently closed),the elements of the device subject to wear like the inner cylinder andthe radiation source can be easily mounted and replaced from the outsideof the device.

According to a preferred embodiment the cylinder parts of the outercylinder assembly include a locking cylinder part at one or at bothaxial end(s), wherein the locking cylinder part(s) is/are arranged toreleasably engage with the end cap(s). Preferrably the releasableengagement is a snap-connection, preferably including plural lockingprotrusions at one of the locking cylinder part and the end cap andmating locking openings at the other one of the locking cylinder partand the end cap.

By providing the releasable engagement between the end cap(s) and theouter cylinder assembly, especially in the form of a snap-connection,the device can be mounted/dismounted without special tools and thenumber of elements forming the device is reduced.

By providing a snap connection with plural locking protrusionsdistributed about the circumference, a substantially uniform highpressure can be applied by the end cap(s) so that the device canwithstand high operating pressures and remains fluid tight. At the sametime the snap-connection provides a repeatable precise holding force sothat O-rings held in place by the end caps(s) are compressed by adefined rated force even if the end cap(s) is/are repeatedlydismounted/mounted for maintenance purposes.

According to a preferred embodiment at least some of the cylinder partsinclude a baffle plate protruding radially inward from an outercylindrical wall.

According to a preferred embodiment the cylinder parts with the baffleplate are substantially cup-shaped with the baffle plate forming anintegral bottom thereof and including a central opening allowing theinner cylinder to be inserted through the axially aligned centralopenings of the cylinder parts.

According to a preferred embodiment the central opening in the bottom ofthe cylinder parts is formed to conform to the outer cross-section ofthe inner cylinder leaving a preferably uniform gap between the outerwall of the inner cylinder and the baffle plate, wherein the gap is theshortest distance between the interface wall and the baffle plate and isequal to or smaller than 2.0 mm, preferably in the range from 1.2 mm to0.3 mm, more preferably in the range from 1.0 mm to 0.5 mm.

The baffle plates create turbulences in the flow of fluid to be purifiedon its route from the inlet to the outlet and force the fluid throughthe narrow gaps between the baffle plates and the interface wall of theinner cylinder to the radiation source received in the inner cylinder,thereby creating a small fluid layer thickness along the interface wall.This small layer thickness is necessary to ascertain that substantiallyall the fluid passing through the device is exposed to the radiation ofthe radiation source. If a mercury free radiation source like an excimerlamp with a relatively low wavelength in the range of 150 nm to 200 nmis used, the radiation has a relatively low transmission through water.Further, the baffles generate just sufficient turbulences in the fluidin the immediate vicinity of the interface wall so that the fluid flowis not laminar but is intermixed without reducing the flow rate alongthe length of the device. The intermixing secures uniform exposure timesof the fluid to the radiation and produces a uniform purity level, i.e.a low TOO, of the fluid that has passed the device and a higher TOOreduction can be achieved for a given flow rate and a given lamp size.

Further, as compared to an existing device, a lower intensity lamp canbe used or lamp ageing is affecting the performance to a smaller extent.Also, the capacity to ionize more complex organics is improved.

Since all the fluid is forced to flow in the narrow zone along theinterface wall by the gaps between the interface wall and the baffleplates which function as constrictions and narrow the fluid flow, acomplete penetration of the radiation through the fluid flow is achievedeven in case the radiation source with light having the relatively lowtransmission through water is used in the device.

The smaller, i.e. thinner the active oxidation layer is, the moreefficiently the TOO concentration can be decreased. Moreover, a smallergap size leads to a better production of turbulences. On the other hand,the pressure drop is increased with smaller gap sizes and longer gaplengths defined by the thickness of the baffle plates. The preferred gapsizes and dimensions provide an optimal balance between the flow rate ofthe fluid and the level of purity in the fluid and thus increase theoverall efficiency of the device. According to a preferred embodiment anO-ring is provided between the one end cap or each end cap and thelocking cylinder part(s) including the baffle so as to fluid-tightlyclose the gap between the baffle and the inner cylinder.

The O-ring provides the effect of fluid-tightly closing the volume ofthe container where the fluid flows and the effect of holding the innercylinder in place in the outer cylinder assembly with a comparativelysimple structure.

According to a preferred embodiment the inter-baffle distance in theflow direction along the interface wall is in the range from 4 to 30 mm,preferably from 10 to 20 mm, more preferably around 10 mm. Preferably,the outer cylinder assembly includes from 2 to 20, preferably 3 or 4cylinder parts including the baffle plates.

The inter-baffle distance and the number of baffles in these ranges havebeen determined to provide the best performance and purificationefficiency at a flowrate of 120 liters per hour through the device. Forhigher flow rates a scale up of the device can be performed simply byadding more cylinder parts to the outer cylinder assembly due to themodular structure.

According to a preferred embodiment the cylinder parts forming the outercylinder assembly are formed from metal, preferably stainless steel, andare respectively formed by deforming (deep drawing) a stamped sheetmaterial.

This embodiment provides the possibility of simply and efficientlymanufacturing the cylinder parts including the baffles in the form ofthe integrated bottom plates of the cup-like parts formed fromstamped-out sheet material like metal. In particular, stainless steel isa preferred material for the use in the pharmaceutical industry, thefood industry and the like and in the context of the present inventionmetal (especially stainless steel) has a good UV stability with respectto the wavelengths of the radiation source and is inert with respect tothe fluids being processed.

Besides the advantage of having UV stability, the metal also providesthe advantage of effectively dissipating heat generated by the operationof the radiation source to the environment, i.e. air. Thus an increasein water temperature can be reduced.

According to a preferred embodiment the interface wall of the innercylinder is formed from or includes quartz glass.

According to another preferred embodiment the device comprises aradiation source for emitting radiation with a wavelength in theUV-range, preferable between 150 nm and 200 nm, preferably an excimerlamp, most preferably an excimer lamp configured to emit radiation witha wavelength of 172 nm±8 nm, wherein the radiation source is located inthe inner cylinder so as to be separated from the fluid in the volume ofthe container by the interface wall.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic section view of a purification device accordingto an embodiment of the present invention;

FIG. 2 is an enlarged view of an area II of FIG. 1;

FIG. 3 is a schematic diagram showing the flow situation in the vicinityof the interface wall between the radiation source (lamp) and theflow-through volume of the container without the baffles;

FIG. 4 is a schematic diagram showing the flow situation in the vicinityof the interface wall between the radiation source (lamp) and theflow-through volume of the container with the baffles on the right and aflow simulation on the left;

FIG. 5 is a diagram showing an intensity of UV-light as a function of awavelength of the light and a penetration depth in water;

FIG. 6 is an enlarged schematic section view of a purification devicewith a stack of baffle plates according to an embodiment of the presentinvention;

FIG. 7 is a perspective view of a self-supporting baffle stack;

FIG. 8 is a side view of a flow-through purification device according toa preferred embodiment; and

FIG. 9 is a cross-section view of the flow-through purification deviceof FIG. 8;

FIG. 10 is a perspective explosion illustration of the flow-throughpurification device of FIG. 8

FIG. 11 is a perspective view of the different cylinder parts used tocompose the modular outer cylinder assembly by welding.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. At first, the general aspects ofthe flow-through purification devices using radiation to effect thepurification will be described.

The device according to the invention is specifically suitable forreducing the TOO content of water to produce pure or ultrapure waterutilizing an oxidization reaction by exposure to UV-light but theconcept of the invention to construct a modular container is not limitedto this field of application and can be generally applied toflow-through devices exposing a stream of fluid to other radiationsources or wavelengths although the invention is particular advantageousfor the purification of water.

An oxidization reaction induced by radiation, which is also known as aphoto-oxidation reaction, can take place in a fluid containing organiccarbon when it is exposed to radiation, in the present context toradiation with a wavelength below 200 nm that can be produced usingexcimer lamps as the radiation source that are free of mercury. Uponexposure to the radiation the organic carbon compounds contained withinthe fluid oxidize and carbonates and byproducts comprising intermediateions other than carbonates are formed.

As schematically shown in FIG. 1, the purification device 1 generallyhas an axially elongated cylindrical container 5 with an outer cylinder5 a which has an inlet 3 for a fluid to be purified located at an axialend portion of the container 5 (on a vertical upper side of the outercontainer 5 a in the posture of FIG. 1), and an outlet 7 for a purifiedfluid located at an opposite axial end portion of the container 5 (on avertical lower side of the outer cylinder 5 a in the posture of FIG. 1).An exposure zone for the fluid to be purified is located between theinlet 3 and outlet 7 and defines an active reactor length. The specificstructure and location of the inlet 3 and outlet 7 is not particularlyrelevant as long as a continuous flow through the exposure zone of thedevice 1 can be created.

In order to make use of the gravitation to force the fluid to flowthrough the exposure zone the device 1 can be arranged such that theinlet 3 is at the vertical upper side and the outlet 7 is located at thevertical lower side as shown in FIG. 1. More preferably, the device 1 isoperated upside down by employing a pump (not shown) to force the fluidfrom an inlet 3 at the vertical lower side of the device 1 up to anoutlet 7 at the vertical upper side in order to efficiently suppressbuilding of air bubbles in the fluid. The vertical posture is preferredas it equalizes the distribution about the circumference where thebaffle plates to be described later are substantially perpendicular tothe longitudinal direction of the container 5.

In this schematic embodiment eight baffle plates 9 are arranged in theexposure zone inside the container 5 outer cylinder 5 a. Each baffleplate 9 has two horizontal surfaces which are substantiallyperpendicular to the longitudinal axis of the outer cylinder 5 a whichcorresponds to the flow direction of the fluid through the container 5.The baffle plates 9 also have a vertical surface parallel to the fluidflow direction and facing a wall (interface wall 11) of an innercontainer or receptacle to be described later. The invention is notlimited to eight baffle plates 9 and may include for example four,preferably eight to twelve baffle plates. The optimum number of baffleplates 9 can be determined in relation to the container length anddiameter, i.e. the desired flow volume. For example, in a device with anexposure zone (active reactor length) of approximately 10 cm and aninner diameter of the outer cylinder of approximately 25 mm 10 baffleplates have been determined to provide optimum performance.

The baffle plates 9 have a thickness T of less than 1.5 mm, preferablyless than 1.0 mm and may be formed from sheet or plate material ofmetal, preferably stainless steel, or from plastics materials that haveUV stability, preferably from fluoropolymer materials, especiallypolytetrafluorethylene (PTFE), PVDF, PEEK, PFA, or polyetherimide (PEI),or PE, preferably provided with a metallic coating.

The baffle plates 9 are, in this embodiment, integrally formed with asurface of an inner peripheral wall 4 of the outer cylinder 5 a and havea centric hole with an inner diameter that is larger than an outerdiameter of the inner cylinder 10 a inserted into the outer cylinder 5 aand sealed in the container such that no fluid can enter the interiorspace of the inner cylinder 10 a. The inner cylinder 10 a thus forms theinterface wall 11 to the exposure zone in the volume 8 of the outercylinder 5.

The inner cylinder 10 a is located concentric inside the outer cylinder5 and forms a receptacle 10 to accommodate a radiation source (excimerlamp) 13 inside and separate it from the exposure zone in the volume 8of the container 5 where the fluid to be purified flows. The interfacewall 11 of the inner cylinder 10 a is therefore permeable at least forradiation with a wavelength in the UV-range, preferable at least between150 nm and 200 nm, more preferably of 172±8 nm.

The baffle plates 9 are arranged with a predetermined distance(inter-baffle distance) D in the axial direction of the container 5between the upstream horizontal surfaces of respective adjacent baffleplates. The inter-baffle distance D in the flow direction between theupstream surfaces along the interface wall 11 is between 4 and 30 mm,preferably between 10 and 20 mm, more preferably around 10 mm.

To meet the transmissivity requirements and UV-stability the innercylinder 10 a or at least the interface wall 11 thereof is preferablymade from or at least includes in relevant portions a quartz materialthat is permeable for radiation in the ultraviolet range, preferably inthe range of at least between 150 nm and 200 nm. Quartz glass (fusedquartz) is formed from silica in amorphous (non-crystalline) form anddiffers from traditional glass in that it does not contain otheringredients which are typically added to glass to lower the meltingtemperature. Quartz glass thus has a high melting point (compared toordinary glass), a high chemical purity and resistance, a high thermalresistance, a low thermal expansion with high resistance to thermalshocks, and a high radiation resistance. The fused quartz preferablyused is a synthetic fused quartz. Furthermore, the (synthetic) fusedquartz may comprise a certain content of hydrogenmonoxid (OH) thatprevents solarisation in the UV-range and has some absorption peaks inthe infrared range.

The radiation source is an excimer lamp 13 (or “excilamp”) which is asource of ultraviolet light produced by spontaneous emission of excimer(exciplex) molecules. The main wavelength that is emitted by the excimerlamp 13 in operation depends on the working gas filling of the excimerlamp. Eligible working gases producing radiation in the desired rangeare Ar, Kr, I₂, F₂ and Xe₂. Excimer lamps are quasi-monochromatic lightsources that can operate over a wide range of wavelengths in theultraviolet (UV) and vacuum ultraviolet (VUV) spectral regions with highpower spectral density. The operation of excimer lamps is based on theformation of excited dimers (excimers) and the transition from the boundexcited excimer state to a weakly bound ground state resulting in anUV-photon radiation. An excimer lamp radiation wavelength is specifiedby the working gas also known as an excimer molecule. A particularlypreferred excimer lamp for use in the device of the invention is oneusing Xenon gas (Xe₂). The excimer lamp is mercury free, electrodelessand the discharge is based on radiofrequency energy. Thus, this lamp hasno ageing effect linked to the number of ON/OFF switching cycles.Compared to a mercury lamp which requires a preheating time ofapproximately 30 s, the excimer lamp is essentially instantaneouslyoperational, i.e. in less than 10 ms. For example, if the Xenon gas(Xe₂) is used as working gas, the emitted radiation has a mainwavelength of 172 nm. On the other hand, if Krypton is used as theworking gas, the main wavelength would be 146 nm. Moreover, the excimerlamp can be discarded as general electrical waste and does not requirespecial treatment or disposal procedures like mercury lamps.

The main wavelength of the radiation of the excimer lamp 13 preferablyused in the invention is preferably below 200 nm, preferably between 150nm and 200 nm, most preferably 172 nm in case pure xenon gas is used,preferably with a half bandwidth of +/−8 nm relative to the peakintensity, wherein there is still more than 50% of the peak intensity inthe range of 164 nm to 180 nm.

Between the interface wall 11 of the inner cylinder 10 a and frontal,i.e. vertical surfaces 9 b of the baffle plates 9 gaps G are formedthrough which the fluid must pass on its way through the exposure zonefrom the inlet to the outlet. These gaps G (as measured in a directionperpendicular to the outer peripheral surface of the interface wall 11,i.e. radial in case of a cylindrical structure, are equal to or smallerthan 2.0 mm, preferably in the range from 1.2 mm to 0.3 mm, morepreferably in the range from 0.5 mm to 1.0 mm.

As shown in FIGS. 2 and 3 the excimer lamp 13 emits radiation, e.g.UV-light, into an area (active oxidation layer) 15 adjacent to theinterface wall 11 in the fluid. Due to the (short) wavelength of theexcimer lamp 13 the intensity of the emitted light decreases quicklywith the increasing penetration depth of the light in the fluid as shownin FIG. 5. Therefore, the size of the gap G between the baffle plates 9and the interface wall is set to a relatively small value in order toirradiate and penetrate the entire thickness of the fluid layer createdby forcing the fluid through the gaps G and along the interface wall 11.Further, since the upper or upstream surfaces 9 a of the baffle plates 9are set to have a right angle with respect to the flow direction alongthe interface wall 11, small turbulences are generated in the fluid. Thesmaller the distance, the higher the turbulences. These internalturbulences intermix the fluid in the active oxidation layer 15 near theinterface wall by forcing parts of the fluid in alternate intervalstoward and away from the interface wall of the inner cylinder 11 andtherefore entering and leaving the active oxidation layer 15. Thus, alaminar flow can be prevented and the entire fluid flow passing thebaffle plates receives substantially the same level of UV exposure. FIG.4 shows a conceptual diagram of the expected flow behavior at flow ratesof 120 l/h (on the right) and the result of a real-life simulation ofthe flow at 40 l/h (on the left). For the invention it is important thatall fluid entering the device 1 must pass through the gaps G, i.e. avoidbypass flows through the volume 8 at portions where the fluid is notexposed to the radiation.

Next a further preferred embodiment will be described with reference toFIG. 6. In FIG. 6 elements like the radiation source, inlet and outletare omitted for convenience of explanation. Different from the aboveembodiment the baffle plates 91 are not integrally formed with the innersurface of the outer cylinder 5 a but the baffle plates 91 are arrangedin a stack with a predetermined spacing (inter-baffle distance) D toform a self-supporting element that is mounted into the internal volume8 of the container 5 (outer cylinder 5 a) so as to surround theinterface wall 11 of the inner cylinder 10 a. In this embodiment theinter-baffle spacing is maintained by spacers 18 which are integrallyformed with a respective one of the baffle plates 91.

In another embodiment shown in FIG. 7 the self-supporting element isformed by baffles made from a sheet material, i.e. stainless steel orplastics material, in the form of disks 92 with a central hole 92 a thatare axially interconnected by bolts 19 serving as spacers arrangedbetween the adjacent disks 92 to maintain a constant inter-baffledistance D and distributed around the circumference. The central hole 92a is dimensioned such that it has a sufficiently larger diameter thanthe outer circumferential wall of the inner cylinder 10 a serving asinterface wall 11 in order to form the desired gaps G for the flow ofthe fluid. The outer periphery of the disks 92 can be sealed against theinner circumferential wall 4 of the outer cylinder 5 by the exactdimensioning of the material resulting in a light press fit of theelement into the outer cylinder 5, by a certain resiliency (in case ofplastics material where the discs are dimensioned slightly larger thanthe cross section of the outer cylinder) or by separate seals attachedto the outer peripheral edges.

For a stable support a minimum of three bolts 19 in a regulardistribution would be sufficient but more can be used. This embodimentis not limited to the shown solution and different combinations ofspacers 18 and connecting means are possible to achieve the“ladder-like” structure of the self-supporting baffle element. Thestructure does not necessarily have to be self-supporting in a rigidmanner. It should just provide sufficient stability that it can beinserted, as a pre-mounted unit, into the outer cylinder 5 a of thecontainer 5 and seal with respect to the inner peripheral surface 4thereof while maintaining the gap G to the inner cylinder 10 a and theinter-baffle distance D. Once inserted the baffles 91,92 will bemaintained in position in the outer cylinder 5 a. Another modificationthat provides reduced assembly time and cost would be to punch outbaffle discs 92 from a sheet material which have a number of lugs orstrips integrally radially protruding from the outer periphery. Theselugs or strips can be subsequently bent from the plane of the discs andcan then serve as spacers 18 to maintain the inter-baffle distance D.The discs with the lugs can be inserted into the outer cylinderunconnected or the lugs can serve to connect the adjacent discs witheach other beforehand to form a unit. The self-supporting modularizedconstruction can reduce the manufacturing and maintenance cost andeffort and can provide a large number of variants of the device 1 with areduced number of different parts. The self-supporting baffle elementcan be used with the modular concept of the invention in that the outercylinder assembly is formed from cylinder parts (as described in detailbelow) that are essentially ring shaped without integrated baffleplates.

The FIGS. 8, 9 and 10 show an actual example of the device of theinvention in a side view from the outside, in a partial cross sectionalview and in an explosion illustration without showing the excimer lamp.The FIG. 11 shows the various cylinder parts from which the device ofthe invention is composed. The various elements of the device areidentified with the same reference signs as in the previously describedschematic embodiments.

The container 5 is formed with a plurality of axially arranged cylinderparts 5 b, 5 c, 5 d and 5 e connected to each other by welding to formthe peripherally fluid-tight outer cylinder 5 a (outer cylinderassembly). Preferably the cylinder parts are connected to each other byTungsten Inert Gas (TIG) welding. TIG welding is an arc welding processthat uses a non-consumable tungsten electrode to produce the weld andthat can be performed together with or without a filler metal, wherebythe latter case is known as autogenous welding and is the mostpreferable welding method for the embodiment. The weld zone is protectedfrom atmospheric contamination by an inert shielding gas which leads tostrong and clean connections, and the TIG welding provides a high levelof process control and is thus especially suitable for thin materials tobe welded. Here, orbital welding is the most preferred welding methodfor the TIG welding due to the cylindrical shape of the cylinder partsthat are to be connected. In orbital welding the arc is mechanicallyrotated through 360° around a static work piece.

The cylinder parts 5 e forming the exposure zone of the outer cylinder 5a have the baffle plates 9 integrally formed and protruding radiallyinward from an outer cylindrical peripheral wall 6 a in the form of abottom plate 6 c provided with a central hole 6 b. The dimension of thecentral hole 6 b relative to the outer dimension of the inner cylinder10 a inserted into the aligned central holes defines the size of the gapG described above through which the fluid is to flow along the interfacewall 11 formed by the inner cylinder.

The inlet 3 and outlet 7 (not visible in the rotated position in FIG. 9)are formed on separate cylinder parts 5 c, 5 d placed adjacent to theaxial end portions of the outer cylinder 5 a defining the oxidation zoneand are attached to the peripheral wall 6 a of the cylinder partsforming the exposure zone by separate connectors or are integrallyconnected by welding (as shown in FIGS. 8 and 9).

Two end caps 20, 21, each one arranged to close one of the two axialends of the outer cylinder 5 a, are releasably engaged with lockingcylinder parts 16 (or 5 b), 17 (or 5 b) of the outer cylinder 5 athrough a snap-connection (described later). The end caps thus fluidtightly close the inner volume 8 of the cylinder 5 where the fluid flowsat the axial ends thereof to the environment.

The cylinder parts 5 b, 5 c and 5 e connected to each other by weldingat the axial peripheral rims 6 d to form the fluid-tight outer cylinder5 a (outer cylinder assembly) can—except the cylinder part 5 d—all havethe same basic “cup- or pot-like” design and essentially identical outerdimensions. For this basic design the cylinder parts 5 b, 5 c and 5 eare respectively formed from metal, preferably stainless steel, bydeforming (deep drawing) a stamped sheet material into the “cup- orpot-like” form where the bottom 6 c forms the baffle plate 9 and theperipheral circumferential wall 6 a forms part of the outer wall of theouter cylinder 5 a. Beside the advantage of UV stability metal alsoprovides the capability of dissipating heat generated by the operationof the radiation source to the environment, i.e. air. Thus an increasein water temperature can be suppressed.

The locking cylinder parts 16, 17 (5 b) are cylinder parts with the“cup- or pot-like” design similar to the cylinder parts 5 e forming theexposure zone and the cylinder part 5 c provided with the inlet with thedifference of having four holes 25 serving as locking openings in theperipheral wall. The locking cylinder parts 16, 17 (5 b) in theembodiment are identical but are connected in the outer cylinder 5 a inopposite orientation so that their bottom is in both cases located tothe inside.

This necessitates the use of a single different cylinder part 5 d thatcan be identical to the other “cup- or pot-shaped” cylinder parts withrespect to the peripheral circumferential wall 6 a but has no bottom 6c. In this case the outlet 7 is provided on this ring-shaped cylinderpart 5 d. Of course, it is also possible to use the ring-shaped cylinderpart (without the bottom) instead of one of the cylinder parts 5 eforming the exposure zone and to orient the adjacent cylinder part, beit a cylinder part 5 e or a cylinder part 5 c with an inlet/outlet, withthe bottom in an inverted orientation in the stack of cylinder partsforming the outer cylinder 5 a.

Typical dimensions of the “cup- or pot-like” cylinder parts to form theflow-through purification device include an outer diameter between 10 cmand 3 cm, preferably 4 cm and the diameter of the central hole 6 b foraccommodating the inner cylinder 10 a (of quartz) can be between 5 cmand 1.5 cm, preferably 2 cm. The outer dimension of the inner cylinderis then selected accordingly to create the gap within the dimensionallimits described above depending on the desired radiation wavelength ofthe radiation source, throughput and purification level.

The end caps 20, 21 have a plug-like design and include a cylindricalannular main body 26 and four elastic legs 24 serving as connectionportions in that they are provided with hook-like protrusions 24 aprotruding radially outward from free ends of the legs 24 arranged toengage with the holes 25 of the locking cylinder parts 16, 17 in orderto releasably attach the end caps to the locking cylinder parts 16, 17.The legs 24 are equidistantly distributed about an outer periphery ofthe cylindrical annular main body 26, protrude upward therefrom and areinclined radially outward. The cylindrical main body of the end cap 20,21 has a slightly smaller outer diameter than an inner diameter oflocking cylinder part 16, 17 and the inner diameter of the main body isslightly larger than the outer diameter of the inner cylinder 10 a. Thelegs are integrally connected to the main body of the end cap 20, 21, sothat the outer diameter of the end cap 20, 21 as a whole becomes largerthan an inner diameter of the locking cylinder part 16, 17. By insertingthe end cap 20, 21 into the locking cylinder part 16, 17 the legs arepressed radially inward against their resiliency and, when the end cap20, 21 is fully inserted into the respective locking cylinder part 16,17 and the hook-like protrusions 24 a are aligned with the respectiveholes, the protrusions snap, i.e. click into place in the respectiveholes of the end cap 20, 21 and are form-locking held in the holes.

The pressure inside the container, i.e. the occurring reaction forcesdue to this pressure are acting on the connection portions. Therefore,the dimensions of the projections, their form and the strength andelasticity of the legs and their number have to be selected to withstandthese forces and to avoid that the legs break or that the projectionsslip out of the holes in operation. The pressure inside the container inoperation can be up to 24 bar which is equivalent to 3000N acting on theconnection portions. The invention is not limited to four legs ofcourse. The end caps can be formed as an integral component fromplastics material, preferably those that have UV stability as thematerials described above in connection with the baffle plates.

Before the end caps 20, 21 are inserted the inner cylinder 10 a servingas receptacle for the radiation source (excimer lamp) 13 is insertedinto the outer cylinder 5. The excimer lamp 13 can be inserted into theinner cylinder before or after the same is inserted into the outercylinder. The excimer lamp can be fixed in the inner cylinder bysuitable connectors, be it releasable or fixed. As shown in FIGS. 8 and9 the excimer lamp 13 has electrical connectors 13 a protruding from oneof the axial end portions of the device 1 so that current for operatingthe same can be applied.

Before the end caps are inserted an O-ring 22, 23 is respectively fit onthe inner cylinder 10 a and put in place until it covers the gapprovided between the central hole in the bottom of the locking cylinderparts 5 b and the inner cylinder 10 a (see FIGS. 9 and 10). When the endcaps are fully inserted and engaged with the locking cylinder parts, theO-ring is compressed in place to provide fluid tightness of the innervolume of the container 5 where the fluid to be processed flows. At thesame time the compressed O-ring also holds and fixes the inner cylinder10 a (receiving the excimer lamp 13) in place in the outer cylinder 5.

Thus, the insertion opening of the inner cylinder for inserting/removingthe excimer lamp 13 is accessible to the outside of the device evenafter closing the inner volume of the container between the inner andouter cylinders by attaching the end caps to facilitate maintenance andmanufacturing. In other words, the entire device can be pre-fabricatedwithout the excimer lamp 13 which can be subsequently mounted to thedevice or the excimer lamp can be changed and/or temporarily removed forcleaning or repairing the other parts of the device. Also, differentradiation sources can be used with the same device provided they fitinto the receptacle formed by the inner cylinder.

The structure of the outer cylinder 5 a being formed from stacked, i.e.axially aligned and welded cylinder parts of substantially identicalbasic design provides advantages with respect to manufacturingsimplicity and cost.

Further, a range of devices with different axial length, capacity andthroughput can be easily set up with a small number of differentcomponents in a modular construction. Devices having a longer axiallength of the oxidation zone can provide a lower TOO of the purifiedwater at the outlet.

As described above the outer cylinder 5 a is closed by providing two endcaps 20, 21 on both axial ends thereof. Nevertheless, it is alsopossible to provide only one end cap 20, 21 at one axial end of theouter cylinder 5 a and to close the other end by providing a furthercylinder part (not shown) having a completely closed bottom andconnected by welding to the penultimate cylinder part in the stack ofcylinder parts forming the outer cylinder 5 a. It is also possible toclose both ends by providing two of this further cylinder part (notshown) having a completely closed bottom and connected by welding to thepenultimate cylinder part in the stack of cylinder parts forming theouter cylinder 5 a. Furthermore, the end cap(s) 20, 21 can also beconnected to the outer cylinder 5 a by other releasable connection meanslike a bajonet- or thread-type connection that provide for anapplication of the required axial force to compress the O-ring or can befixedly attached in a manner that cannot be removed without destruction,i.e. by welding or glueing. However, the axial snap-fit connection ispreferred as it avoids a relative rotational movement between the O-ringand the end cap and produces with repeatability precise levels ofcompression and holding force.

It has to be noted that the advantages of the invention due to themodular construction can be realized in a variety of flow-throughpurification devices independently from using, for example, baffleplates or an excimer lamp as radiation source.

REFERENCES

-   1 device-   3 inlet-   4 inner peripheral wall-   5 outer container-   5 a outer cylinder-   5 b, 5 c, 5 d, 5 e cylinder parts-   6 a peripheral wall-   6 b central hole-   6 c bottom plate-   6 d peripheral rim-   7 outlet-   8 volume-   9,91 baffle plate-   10 receptacle-   10 a inner cylinder-   11 interface wall-   13 radiation source (excimer lamp)-   15 active oxidation layer-   16, 17, 5 b locking cylinder part-   18 spacers-   19 bolts-   20, 21 end cap-   22, 23 O-ring-   24 leg-   24 a projection (locking protrusion)-   25 hole (locking opening)-   26 annular main body-   D inter-baffle distance-   G gap-   T thickness

1. A flow through fluid purification device comprising: a containerarranged such that fluid can flow through a volume of the container froman inlet to an outlet; and an inner cylinder inserted or insertable intothe volume of the container and defining an interface wall permeable forradiation with a wavelength in the UV-range, preferably between 150 nmand 200 nm, wherein the container includes a plurality of axiallyarranged cylinder parts connected to each other by welding to form anouter cylinder assembly.
 2. The device according to claim 1, wherein thedevice has one end cap engaged with an open axial end of the outercylinder assembly to fluid tightly close the volume of the container atthe end where the end cap is arranged and to hold the inner cylinder inposition in the outer cylinder assembly.
 3. The device according toclaim 1, wherein the device has two end caps, each one engaged with oneof the two open axial ends of the outer cylinder assembly to fluidtightly close the volume of the container at the ends, wherein at leastone of the two end caps is arranged to hold the inner cylinder inposition in the outer cylinder assembly.
 4. The device according toclaim 2, wherein the cylinder parts of the outer cylinder assemblyinclude a locking cylinder part at one or at both axial end(s), whereinthe locking cylinder part(s) is/are arranged to releasably engage withthe end cap(s).
 5. The device according to claim 4, wherein thereleasable engagement is a snap-connection.
 6. The device according toclaim 1, wherein at least some of the cylinder parts include a baffleplate protruding radially inward from an outer cylindrical wall.
 7. Thedevice according to claim 6, wherein the cylinder parts with the baffleplate are substantially cup-shaped with the baffle plate forming anintegral bottom thereof and including a central opening allowing theinner cylinder to be inserted through the axially aligned centralopenings of the cylinder parts.
 8. The device according to claim 7,wherein the central opening in the bottom of the cylinder parts isformed to conform to the outer cross-section of the inner cylinderleaving a preferably uniform gap between the outer wall of the innercylinder and the baffle plate, wherein the gap is the shortest distancebetween the interface wall and the baffle plate and is equal to orsmaller than 2.0 mm.
 9. The device according to claim 8, wherein anO-ring is provided between the at least one end cap and the lockingcylinder part(s) including the baffle so as to fluid-tightly close thegap between the baffle and the inner cylinder.
 10. The device accordingto claim 6, wherein the inter-baffle distance (D) in the flow directionalong the interface wall is in the range from 4 to 30 mm.
 11. The deviceaccording to claim 6, wherein the outer cylinder assembly includes from2 to 20 cylinder parts including the baffle plate.
 12. The deviceaccording to claim 1, wherein the cylinder parts forming the outercylinder assembly are formed from metal, and are respectively formed bydeforming a stamped sheet material.
 13. The device according to claim 1,wherein the interface wall of the inner cylinder is formed from orincludes quartz glass.
 14. The device according to claim 1, furthercomprising a radiation source for emitting radiation with a wavelengthin the UV-range, wherein the radiation source is located in the innercylinder so as to be separated from the fluid in the volume of thecontainer by the interface wall.
 15. The device according to claim 5,wherein the snap-connection includes plural locking protrusions at oneof the locking cylinder part and the end cap and mating locking openingsat the other one of the locking cylinder part and the end cap.
 16. Thedevice according to claim 14, wherein the radiation source emitsradiation with a wavelength between 150 nm and 200 nm.
 17. The deviceaccording to claim 14, wherein the radiation source is an excimer lampconfigured to emit radiation with a wavelength of 172 nm±8 nm.